Temperature measuring probe and electronic clinical thermometer equipped with same

ABSTRACT

Provided are a temperature measuring probe separable from a main body which includes a signal processor, and an electronic clinical thermometer equipped with this probe. The temperature measuring probe includes a temperature measuring circuit supported by a flat, flexible, strip-shaped base member, in which the temperature measuring circuit is sealed by a coating member, such as a film, and/or a filler, one end thereof being treated to form a connector. This structure allows the overall probe to be formed into a film-, sheet- or plate-like configuration. Preferably, a core member is provided between the base member and coating member, with the flexibility and rigidity of the overall probe being decided by selecting the thickness, material and cross-sectional configuration of the core. The temperature measuring circuit preferably is composed of the minimum number of required circuit elements, and individual probes are provided with interchangeability by trimming, selection of characteristics or other treatment.

This invention is a continuation of application Ser. No. 07/658,980filed Feb. 21, 1991, now abandoned, which is a application Ser. No.07/396,540 filed Aug. 21, 1989, now U.S. Pat. No. 5,088,837.

BACKGROUND OF THE INVENTION

This invention relates to a temperature measuring probe and anelectronic clinical thermometer equipped with the probe. Moreparticularly, the invention relates to a temperature measuring probeseparable from a main body which includes a signal processor, and theelectronic clinical thermometer equipped with this probe.

In a conventional electronic clinical thermometer, a main body whichincludes a signal processor is unitary with a probe. The overallthermometer is rigid and the probe portion thereof is rod shaped Forthis reason, the temperature sensing portion has a large thermalcapacity, so that it is difficult to shorten temperature measurementtime.

In addition, when an electronic clinical thermometer of thisconventional type is inserted in an armpit, clothing can become animpediment to measurement. When the thermometer is placed in the mouth,it causes discomfort under the tongue.

When a conventional electronic clinical thermometer is of the type usedfor measuring body temperature orally or anally, a troublesomesterilization operation or the like is required owing to the risk ofinfection. As a result, the popularity of such thermometers is reducedfor reasons of hygiene and cleanliness.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a novel,disposable temperature measuring probe, and an electronic clinicalthermometer having the probe, in which the temperature sensing portionhas excellent thermal response and the probe is easy to handle whenmeasuring various parts of the body.

In order to attain the foregoing object, the temperature measuring probeof the invention includes a temperature measuring circuit supported by aflat, flexible, strip-shaped base member, in which the temperaturemeasuring circuit is sealed by a coating member, such as a film, and/ora filler, one end thereof being treated to form a connector.

In a preferred embodiment, the temperature measuring circuit includes atemperature sensing body and a conductor for leading an electric signalfrom the temperature sensing body to the exterior of the temperaturemeasuring circuit.

In a preferred embodiment, the temperature measuring circuit includes atemperature sensing body, a precision compensating resistor or alinearizing resistor for the temperature sensing body, and a conductorfor leading electric signals from these elements to the exterior of thetemperature measuring circuit.

In a preferred embodiment, the temperature sensing body is a thermisteror a thin-film body made of platinum or the like.

In a preferred embodiment, the precision compensating resistor orlinearizing resistor is a thin-film resistor.

In a preferred embodiment, the temperature sensing body is sealed by afiller having excellent thermal conductivity and is exposed from thecoating member.

In a preferred embodiment, a core member is provided between the basemember and the coating member.

In a preferred embodiment, the core member has a thickness approximatelythe same as those of circuit elements of the temperature measuringcircuit and is formed to include cavities for receiving the circuitelements.

In a preferred embodiment, the core member has one or more polygonal orcircular cavities at portions other than those corresponding to thecircuit elements

In a preferred embodiment, the core member resides only at a peripheralportion of the temperature sensing body and has a smoothly diminishingthickness.

In a preferred embodiment, at least the cavity for the temperaturesensing body is filled with a filler having excellent thermalconductivity.

In a preferred embodiment, an adhesive portion is provided on a portionof a surface of the probe.

Further, in order to solve the foregoing object, there is provided anelectronic clinical thermometer having the above-described temperaturemeasuring probe removably attached thereto.

Basically, therefore, the temperature measuring probe of the presentinvention possesses a structure in which a temperature measuring circuitis supported by a flat, flexible, strip-shaped base member and is sealedby a coating material, such as a film, and/or a filler. This makes itpossible to form the overall probe into a film-shaped member (having athickness of 0.05-0.2 mm), a sheet-shaped member (having a thickness of0.2-1.0 mm) or a plate-shaped member (having a thickness of 1.0-4.0 mm).As a result, thermal capacity at the periphery of the temperaturesensing body is reduced and, at the same time, the thermal resistance tothe exposed portion at the time temperature is sensed is enlarged,thereby making it possible to shorten temperature sensing time.Furthermore, since the probe is made of a flexible material and is flatin shape, flexibility is maintained in a direction perpendicular to thesurface whose temperature is measured (i.e., in the direction of thesurface on which the probe is used) while there is almost no flexibilityin a direction parallel to the surface (i.e., in the direction laterallyof the surface). When temperature is measured, therefore, the flat probeassumes an attitude inserted in or affixed to the body part measured, atwhich time the rigidity in the lateral direction and the flexibility inthe direction of the surface on which the probe is used assure that theprobe can be inserted or affixed with ease and that the probe will bestably maintained after being set in place.

Preferably, the temperature sensing circuit is composed of the minimumnumber of required circuit elements. For example, the probe is providedwith interchangeability by such processing as trimming of thetemperature sensing body and/or the precision compensating resistorand/or the linearizing resistor or selection of the precisioncompensating resistor and/or the linearizing resistor. The probe canthus be made disposable.

Preferably, the temperature sensing body is sealed in a filler havingexcellent thermal conductivity and is exposed from the coating member toimprove the thermal response of the temperature sensing portion.

Preferably, a core member is stacked between the base member and thecoating member. Flexibility and rigidity are freely selected byselecting the thickness, material and cross-sectional shape of the coremember.

Preferably, the core member has approximately the same thickness asthose of the circuit elements of the temperature measuring circuit, andportions of the core member corresponding to the circuit elements areformed into cavities to protect the circuit elements. The probe coatingof film or the like is formed to have overall smoothness.

Preferably, the core member is provided with one or more polygonal orcircular cavities at portions other than those corresponding to thecircuit elements. This reduces the amount of heat that escapes from thetemperature sensing portion via the core member. Thermal response isimproved.

Preferably, the core member is provided only at a peripheral portion ofthe temperature sensing body and has a smoothly diminishing thickness.This protects the temperature sensing body and smoothens the coating,made of film or the like, of this portion.

Preferably, at least the cavity which receives the temperature sensingbody is filled with a filler having excellent thermal conductivity,thereby improving the thermal characteristics of the temperature sensingbody. This also protects the temperature sensing body against thepenetration of chemicals, saliva and the like.

Preferably, an adhesive portion is provided on a portion of the surfaceto stabilize and retain the probe after it is affixed.

The electronic clinical thermometer of the invention has theabove-described temperature measuring probe removably attached thereto.By arranging it so that signal processing is performed through anappropriate method, the probe can be made disposable.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view illustrating a first embodiment of a temperaturemeasuring probe according to the invention;

FIG. 2 is a sectional view taken along line A--A of FIG. 1;

FIG. 3 is a sectional view taken along line B--B of FIG. 1;

FIG. 4 is a front view illustrating a second embodiment of a temperaturemeasuring probe according to the invention;

FIG. 5 is a sectional view taken along line C--C of FIG. 4;

FIG. 6 is a sectional view illustrating a third embodiment of atemperature measuring probe according to the invention;

FIG. 7 is a sectional view illustrating a modification of the thirdembodiment;

FIGS. 8 through 10 are sectional views of other embodiment relating tothe B--B cross-sectional configuration of FIG. 3;

FIG. 11 is a sectional view illustrating a fifth embodiment of atemperature measuring probe according to the invention;

FIG. 12 is a sectional view illustrating a sixth embodiment of atemperature measuring probe according to the invention;

FIGS. 13 and 14 are back views illustrating a seventh embodiment of atemperature measuring probe according to the invention;

FIG. 15 is a view showing a case where the probe of FIG. 13 is used fororal temperature measurement;

FIGS. 16(A), (B) are views showing a case where the probe of FIG. 14 isused for armpit temperature measurement;

FIG. 17 is a circuit diagram showing a temperature measuring circuit fora case where measurement performed by an electronic clinical thermometeris of the oscillatory type;

FIG. 18 is a circuit diagram showing a temperature measuring circuit fora case where measurement performed by an electronic clinical thermometeris of the constant-current type;

FIG. 19 is an external perspective view showing an embodiment of anelectronic clinical thermometer of the oscillatory type; and

FIG. 20 is a block diagram illustrating an embodiment of an electronicclinical thermometer according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

A first embodiment of the invention relates to a temperature measuringprobe in which the circuit elements possess thickness.

FIG. 1 is a front view illustrating the first embodiment of thetemperature measuring probe according to the invention, FIG. 2 is asectional view taken along line A--A of FIG. 1, and FIG. 3 is asectional view taken along line B--B of FIG. 1. As shown in FIGS. 1through 3, a temperature measuring circuit is mounted on a base member 2and comprises a thermister 4 serving as a temperature sensing body, aprecision compensating resistor or linearizing resistor 5, and aconductor 3 for leading electric signals from these elements to theoutside of the probe Stacked on the base member 2 is a core member 6having cavities 100, 101 corresponding to the thermister 4 and resistor5, respectively. At least the cavity 100 is filled with a filler 7having a high thermal conductivity. The top of this arrangement iscoated with a coating 8 such as film. In order to provide electricalconnection to the main body of an electronic clinical thermometer, theterminus of the conductor 3 is not covered by the core 6 or film 8 butis left exposed to form a connector portion 9.

Employed as the base member 2 is polyimide, polyester or the likeexhibiting heat resistance to soft solder. An example of the corematerial 6 is polyethylene or the like that has been subjected to asurface treatment. An example of the film 8 is polyester or the like.The core material 6 has a thickness approximately the same as that ofthe thermister 4 or resistor 5, serves to protect these circuit elementsand is such that the coating provided by the film 8 can be performedeasily and smoothly. The thickness, shape and material of the core 6 canbe freely selected so that the probe can be provided with the properrigidity Alternatively, the core material 6 at the probe end E can bethinned somewhat to make it easier for this probe end to be inserted ina body cavity, such as the mouth, where temperature is to be measured.

The base member 2, core material 6 and film 8 are electrical insulatorsfor the purpose of protecting the temperature sensing body, conductorand the like, and these are required to exhibit some water resistanceand resistance to chemicals (disinfectants).

An example of the filler 7 is an epoxy adhesive or the like.

Overall, the probe has a flat, strip-shaped configuration and can beformed into a sheet (having a thickness of 0.2-1.0 mm) or a plate(having a thickness of 1.0-4.0 mm). As a result, thermal capacity at theperiphery of the temperature sensing body is reduced and, at the sametime, the thermal resistance to the exposed portion at the timetemperature is sensed is enlarged, thereby making it possible to shortentemperature sensing time. Furthermore, since the probe is made of aflexible material and is flat in shape, there is flexibility in adirection perpendicular to the surface whose temperature is measured(i.e., in the direction of the surface on which the probe is used) whilethere is almost no flexibility in a direction parallel to the surface (ie., in the direction laterally of the surface). When the temperature ofthe mouth is measured, therefore, the flat probe assumes an attitudeinserted under the tongue, at which time the rigidity in the side-facedirection makes it difficult for warping to occur while the flexibilityin the direction of the surface used makes it possible to insert theprobe where desired. After the probe is inserted, the flexibility in thedirection of the surface used can be utilized to allow the probe to bandso that it will not become an obstruction.

It should be noted that the base member 2 and conductor 3 can bereplaced by a flexible substrate, in which case the base member 2 wouldcomprise a thermoplastic resin exhibiting thermal resistance at themelting point of soft solder, an example being polyimide or polyester.The materials constituting core 6 and film 8 are chosen upon taking intoconsideration such factors as their adhesion, weldability andfusibility.

The resistor 5 and cavity 101 can be eliminated if use is made of athermister 4 precision-compensated as by trimming.

Second Embodiment

The second embodiment of the invention relates to a temperaturemeasuring probe in which the amount of heat that escapes via the corematerial is reduced.

FIG. 4 is a front view illustrating a second embodiment of a temperaturemeasuring probe according to the present invention, and FIG. 5 is asectional view taken along line C--C thereof In FIGS. 4 and 5, if thecore material 6 is provided with more than a certain degree ofthickness, the majority of the heat at the periphery of the thermister 4will be transmitted rearwardly of the probe via the core material 6 whentemperature is sensed, and the heat will escape to the outside from theexposed portion Accordingly, in the second embodiment of the invention,triangular cavities 102 are provided at a number of locations so as toreduce the escape of heat longitudinally of the probe via the core 6.The cavities 102 can be circular or polygonal if desired, and one or aplurality can be provided. If the core is sufficiently thin, there willbe little escape of heat to the exposed portion, in which case the coreneed not be provided with holes.

Third Embodiment

The third embodiment of the invention relates to a temperature measuringprobe in which only the temperature sensing body has thickness.

FIG. 6 is a sectional view illustrating a third embodiment of atemperature measuring probe according to the present invention, and FIG.7 is a sectional view showing a modification of the third embodiment. InFIGS. 6 and 7, if a thin-film resistor 10 is employed as the precisioncompensating resistor or the linearizing resistor, it is not alwaysnecessary to adopt a laminated structure in which the core 6 isinterposed between layers. As a result, in the third embodiment, thecore 6 is provided solely at the peripheral portion of the thickthermister 4, the core 6 has a thickness approximately the same as thatof the thermister 4 at the portion near the thermister 4. The thicknessof the core 6 diminishes from this portion toward the rearward end ofthe probe. The core 6 is thus tapered in such a manner that it will notcause discomfort at the body part measured while also allowing the film8 to smoothly and uniformly coat the peripheral portion of thethermister 4. Since the thin-film resistor 10 has almost no thickness,it is held in direct, intimate coating contact with the base member 2 bythe film 8. Thus, since the probe of the third embodiment has thicknesssolely at its temperature sensing portion, the user can readilyascertain the location of the temperature sensing portion and performmeasurement with ease.

Rather than providing projections solely on one surface of the probe, atapered structure can be adopted in which the base member 2 is bent atportions D and F.

The resistor 10 can be dispensed with if the thermister 4 isprecision-compensated as by trimming.

There is also a case in which there are a plurality of the precisioncompensating resistors 10 rather than just one (FIG. 18). However, if itis so arranged that the resistors 10 are obtained as by vapordeposition, the number of parts and the mounting process will be nodifferent from when there is only one resistor. Only a process such astrimming for adjusting the precision compensating resistors 10 will bedifferent. If the manufacturing cost per probe can thus be held down,the measuring system of the main body of the electronic clinicalthermometer can be diversified, as by being made an oscillatory systemor direct-current system, so that the measuring system can be providedwith flexibility.

Fourth Embodiment

The fourth embodiment relates to several other embodiments concernedwith the B--B cross section of the probe of the first embodiment.

FIGS. 8 through 10 are sectional views of other embodiments relating tothe B--B cross of FIG. 3. The configurations of the base member 2 andfilm 8 may be as shown in FIG. 8 or 9. In comparison with thearrangement of FIG. 3, here the film 8 is bonded, welded or fuseddirectly to the base 2, and the surface of adhesion to the core 6 isgreater in area. The probe therefore has an improved seal. The crosssection of the probe need not always be rectangular. For example, if thecross section of the core 6 is of the type shown in FIG. 10, thesecondary moment of the cross section can be enlarged.

Fifth Embodiment

The fifth embodiment relates to a probe in which the temperature sensingbody is exposed from the coating by being sealed using a fillerexhibiting high thermal conductivity.

FIG. 11 is a cross sectional view of a fifth embodiment of thetemperature measuring probe according to the present invention. Thoughthe thermister 4 and the precision compensating resistor and/orlinearizing resistor 5 have thickness, these are each coated by thefiller 7 and are sealed and protected thereby. Other portions are coatedwith the film 8. Adopting this arrangement improves the thermal responseof the thermister 4.

It should be noted that the core 6 may or may not be provided.

In addition, the same structure can be obtained even if the temperaturesensing body 4 and/or resistor 5 do not have thickness.

Sixth Embodiment

The sixth embodiment relates to a temperature measuring probe in whichthe temperature sensing body does not possess thickness

FIG. 12 is a sectional view showing a sixth embodiment of a temperaturemeasuring probe according to the present invention By way of example,here the temperature sensing body itself is made of a thin-filmtemperature sensing body 11 consisting of platinum or the like, and thebody 11 per se is precision-compensated as by trimming. If thisarrangement is adopted, it will be unnecessary to provide precisioncompensating resistors, thereby allowing the number of parts to bereduced. As a result, the structure of the probe according to the sixthembodiment is such that the entirety of the base 2, with the exceptionof the connector portion 9, is directly coated with the film 8 withoutthe intervention of the core 6. This facilitates coating. In addition,the probe with this structure is such that thickness and rigidity aredecided by the base 2. The probe can be formed into a film (having athickness of 0.05-0.2 mm), a sheet (having a thickness of 0.2-1.0 mm) ora plate (having a thickness of 1.0-4.0 mm).

Seventh Embodiment

A seventh embodiment relates to a temperature measuring probe having anadhesive portion provided on a part of the probe surface.

FIGS. 13 and 14 are back views illustrating a seventh embodiment of atemperature measuring probe according to the invention. Here theillustrated temperature measuring probe itself employs the arrangementof the first embodiment. The same is true of the other embodiments ofthe probes to follow. By applying an adhesive to a suitable portion ofthe back surface (or front surface) of the probe, this portion can beaffixed to a surface of the human body. Accordingly, a connector andcord for providing the electrical connection to the main body can befixed and supported and will not impede the sensing of temperature.

In the case of FIG. 13, an adhesive portion 21 is provided on all orpart of the portion of the probe back surface extending longitudinallyfrom the center line 20 of the probe as seen from the temperaturesensing body. By virtue of this arrangement, the probe can beconveniently fixed to and supported on a body surface when temperatureis sensed orally.

In the case of FIG. 14, the adhesive portion 21 is provided on all orpart of the portion of the probe back surface at the distal end of theprobe remote from the center line 20 in the longitudinal direction. Thisportion of the probe includes the vicinity of the temperature sensingbody. This arrangement is advantageous in that the temperature sensingportion will not shift when temperature is sensed in an armpit.

FIG. 15 is a view for a case where the probe of FIG. 13 is used tomeasure temperature orally. The temperature sensing portion at the tipof the probe is placed under the tongue, after which the main body ofthe probe is bent toward the chin and affixed thereto by the adhesiveportion 21 at the back surface of the probe. This arrangement allows aconnector 14 and cable 15 to also be restrained and secured below theprobe so as not to interfere with measurement.

FIGS. 16(A) and 16(B) are views for a case where the probe of FIG. 14 isused to measure temperature in an armpit. FIG. 16(A) shows how the backsurface of the temperature sensing portion at the probe tip is affixedin the armpit, and FIG. 16(B) shows the probe in a state held lightly inthe armpit after the probe is affixed. This assures that the temperaturesensing portion will not shift during temperature measurement.

Temperature Measuring Circuit

In order for a probe to be disposable, probe interchangeability isrequired. In order to maintain this interchangeability, precisioncompensation of the temperature sensing body must be performed for eachprobe. To this end, two methods are available. In one method, aninexpensive temperature sensing body and one or more precisioncompensating resistors are mounted on the probe and the precisioncompensating resistors are adjusted. In the other method, only anexpensive temperature sensing body having high precision is mounted onthe probe.

FIG. 17 is a circuit diagram illustrating a temperature measuringcircuit in a case where an electronic clinical thermometer performsmeasurement using an oscillatory method. According to the so-calledoscillatory method, a circuit having a reference resistor R₁ (=theprecision compensating resistor 5), the value whereof does not changewith temperature, and a circuit having the thermister 4 arealternatingly connected and disconnected, an oscillator is caused tooscillate in the main body, the oscillations are counted and temperatureis calculated based on the value of the count Accordingly, theresistance value of the reference resistor R₁ is tuned in advance to theresistance value R_(o) of the thermister 4 at a predeterminedtemperature T_(o) as by trimming.

FIG. 18 is a circuit diagram illustrating a temperature measuringcircuit for a case where an electronic clinical thermometer performstemperature measurement by a constant-current method. Here theresistance values R₂, R₃, R₄ of a plurality of precision compensatingresistors 5-1, 5-2, 5-3 are each adjusted beforehand by trimming or thelike.

If the temperature sensing body itself is precision compensated, theprecision compensating resistors will no longer be necessary.

Electronic Clinical Thermometer

FIG. 19 is an external perspective view illustrating an embodiment of anelectronic clinical thermometer of the oscillatory type. Numeral 16denotes the main body of the electronic clinical thermometer, andnumeral 17 denotes a liquid-crystal display which displays measured bodytemperature. Numeral 15 designates a probe cable capable of being freelywithdrawn from the interior of the main body 16. A connector 14 isprovided at the end of the cable 15. Numeral 1 denotes the temperaturemeasuring probe of the foregoing embodiments.

FIG. 20 is a block diagram showing the construction of an embodiment ofan electronic clinical thermometer according to the present invention.In FIG. 20, the probe 1 includes a thermist R_(th) and a precisioncompensating resistor (reference resistor) R_(s) which has beensubjected to trimming or the like. The temperature measuring circuitcomprising these resistors R_(th), R_(s) is connected to an oscillatorcircuit 35 of the main body 16 via the connector 9 of the probe 1, theconnector 14 of the cable 15 and the cable 15. The oscillator circuit 35comprises a C-MOS inverter I, a capacitor C, an analog switch (ASW) forswitchingly connecting the resistor R_(s) or R_(th) to the oscillatorcircuit in response to a control signal from a CPU, and a resistor Rwhich protects the C-MOS inverter I. The oscillator circuit 35constitutes a portion of an A/D converter circuit More specifically, theA/D converter circuit comprises a reference clock oscillator (OSC) 38which oscillates at a fixed frequency f_(o) (e.g., 1 MHz), a counter(CT) 36 for counting a predetermined number N₁ of pulses in a pulsetrain f_(s) generated when the resistor R_(s) is connected to theoscillator circuit 35, and an up-down counter (U/D-CT) 39 for countingup the pulses in a reference pulse train f_(o) generated by thereference clock oscillator 38 for a time period T during which the CT 36counts the predetermined number N₁, and for counting down the samereference pulse train f_(o) until the value of the count reaches "0".The CT 36 counts the pulses in a pulse train f_(th), generated when theresistor R_(th) is connected to the oscillator circuit 35, for a periodof time (equal to T) during which the U/D-CT 39 is counting down to "0".The A/D converter circuit is controlled by a CPU 31. The latter executestemperature measurement control periodically in response to atimer-interrupt signal TIS having a period of, e.g., 1 sec, which is theresult of frequency-dividing the reference pulse train f_(o) by acounter (CT) 40. In other words, the CPU 31 executes temperaturemeasurement processing (not shown) the program for which is stored in aROM 32. A RAM 33 temporarily stores the temperature data as well asother data necessary for measurement processing. The ROM 32 stores acorrelation table, which is created by using a reference thermister,containing detected temperature values and digital display values havinga predetermined relationship with respect to the detected temperaturevalues. Numeral 34 denotes a driver circuit (LCD-DR) for driving theliquid-crystal display device (LCD) 17. Numeral 41 denotes a batterycircuit which starts supplying power in response to depression of apower supply switch 22, and which stops supplying power in response to asignal from the CPU 31.

The principle of operation of an electronic clinical thermometer havinga disposable probe will now be described in accordance with thearrangement of FIG. 20. When the analog switch ASW is switched over tothe R_(s) side, the oscillation frequency f_(s) is given by thefollowing equation, in which k is a proportional constant:

    f.sub.s =1/kCR.sub.s                                       (1)

The oscillation frequency f_(s) does not vary with a change intemperature When the analog switch ASW is switched over to the R_(th),the oscillation frequency f_(th) is given by the following equation:

    f.sub.th =1/kCR.sub.th                                     (2)

The temperature-resistance characteristic of the resistor R_(th) isgiven by the following equation

    R.sub.th =R.sub.o exp[B(1/T.sub.t -1/T.sub.o)]             (3)

R_(o) : thermister resistance value at reference temperature T_(o)

R_(th) : thermister resistance value at certain temperature T_(t)

B: B-constant of thermister

Accordingly, when R_(th) is connected, the oscillation frequency f_(th)depending upon a change in temperature. If the pulse train f_(th) iscounted for a gate time period T_(c) controlled to be a constant value,then the counted value N_(th) will vary in accordance with the followingequation:

    N.sub.th =T.sub.c /kCR.sub.th                              (4)

If the counted value N_(o) at the reference temperature T_(o) is assumedto be

    N.sub.o =T.sub.c /kCR.sub.o                                (5)

then the counted value N_(th) at a certain temperature T_(t) will begiven by the following equation:

    N.sub.th =N.sub.o exp [-B(1/T.sub.t -1T.sub.o)]            (6)

The electronic clinical thermometer performs temperature compensationbased on the foregoing. Specifically, the gate time period T_(G)required for the pulse train f_(s), produced when the resistor R_(s) isconnected, to be counted up to a fixed count N₁ is obtained, then thepulse train f_(th), which is produced when the resistor R_(th) isconnected, is counted for the same time period T_(G), thereby obtaininga counted value N₂. The counted values N₁, N₂ and the gate time periodT_(G) are related as follows:

    T.sub.G =N.sub.1 /f.sub.s =N.sub.2 /f.sub.th               (7)

and the counted values N₁, N₂ are related as follows:

    N.sub.2 =(f.sub.th /f.sub.s)N.sub.1                        (8)

Since the counted value N₂ is obtained by counting for the gate timeperiod T_(G) when the resistor R_(th) has been connected, we have

    N.sub.2 =T.sub.G /kCR.sub.th                               (9)

A counted value N₂₀ at the reference temperature T_(o) is given by thefollowing equation:

    N.sub.20 =T.sub.G /kCR.sub.o                               (10)

Accordingly, the counted value N₂ has a value proportional to the twooscillation frequencies f_(s), f_(th) generated in the two countingoperations, with the counted value N₁ being a predetermined number.Thus, the counted value N₂ is correct at all times and exhibitsexcellent reproducibility.

Accordingly, even if a gentle variation with the passage of time or avariation with temperature appears in the circuit characteristics withthe exception of R_(s) and R_(th), a cancelling effect takes place withregard to the counted value N₂. This makes it possible to provide ahighly precise, highly stable electronic clinical thermometer. Iftrimming or the like is carried out in such a manner that the value ofR_(s) becomes comparatively close to the resistance value R_(tho) of thethermister R_(th) at the time of the reference temperature T_(o), thenthe counted value N₂₀ can be replaced by the counted value N₁ tosimplify the apparatus. Accordingly, the electronic clinical thermometerof this embodiment is equipped with the resistor R_(th) or R_(s) trimmedfor each replaceable probe. To this end, the thermometer is handled asone in which the counted value N₂₀ is replaced at all times by thecounted value N₁ on the side of the thermometer main body 16, thusrendering the probe disposable.

In accordance with the present invention as described above, the probehas a flat configuration. As a result, thermal response is excellent andmeasurement time can be shortened.

In addition, since the probe is disposable, there is no risk ofinfection. This will increase the demand for such probes.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An electronic clinical thermometer comprising:amain body for performing signal processing; and a temperature measuringprobe which is removably attached to said main body for performingsignal processing, said temperature measuring probe including a flat,flexible stripshaped base member, a core member secured on said basemember and including a portion having at least one cavity therein, atemperature measuring circuit including a temperature sensing bodypositioned within said at least one cavity of said core member, thethickness of said core member at said portion thereof beingapproximately the same as that of said temperature sensing body, aconductor coupled to said temperature sensing body, a connector formedon one end of said base member, and a coating member on said core memberfor sealing the interior of said probe from the outside.
 2. Anelectronic clinical thermometer according to claim 1, wherein saidconductor is for leading an electric signal from said temperaturesensing body to said main body for performing signal processing.
 3. Anelectronic clinical thermometer according to claim 2, wherein saidtemperature sensing body is one of a thermistor and a thin-film body ofplatinum.
 4. An electronic clinical thermometer according to claim 3,further comprising a filler filling said at least one cavity whichaccommodates the temperature sensing body therein, said filler havingexcellent thermal conductivity.
 5. An electronic clinical thermometeraccording to claim 1, further comprising a filler filling said at leastone cavity which accommodates the temperature sensing body therein, saidfiller having excellent thermal conductivity.
 6. An electronic clinicalthermometer according to claim 1, wherein said temperature measuringcircuit includes at least one of a precision compensating resistor and alinearizing resistor for said temperature sensing body, and saidconductor is for leading electric signals from these elements to saidmain body for performing signal processing.
 7. An electronic clinicalthermometer according to claim 6, wherein said temperature sensing bodyis one of a thermistor and a thin-film body of platinum.
 8. Anelectronic clinical thermometer according to claim 7, further comprisinga filler filling said at least one cavity which accommodates thetemperature sensing body therein, said filler having excellent thermalconductivity.